(a) Field of the Invention
This invention relates to O-alkyl OO-(1,1,3,3-tetramethylbutyl) monoperoxy carbonates and their uses as free-radical polymerization initiators and as free-radical curing catalysts. In the interest of brevity, 1,1,3,3-tetramethylbutyl will be hereinafter usually referred to as t-octyl.
(B) State of the Art
While applicant is not aware of any prior art which reports any of the compounds of this invention or recognizes their superior properties as free-radical initiators and curing catalysts, several patents have disclosed monoperoxycarbonates.
For example, U.S. Pat. No. 2,374,789 prepares O-alkyl OO-alkyl peroxycarbonates from t-butyl and ethyl hydroperoxides. British Patent 1,104,336 discloses the use of O-alkyl OO-t-alkyl peroxycarbonates as initiators for vinyl polymerizations wherein the OO-t-alkyl group can contain up to 6 carbons as in t-hexyl (similar olefin polymerizations are disclosed in British Pat. No. 1,102,067). U.S. Pat. No. 3,326,859 discloses the use of O-alkyl OO-alkyl peroxycarbonates as initiators wherein the preferred OO-alkyl group is t-butyl, t-amyl or .alpha.-cumyl. They also list bismonoperoxycarbonates wherein the O-alkyl group is --CH.sub.2 --CH.sub.2 -- or isopropyl and the OO-alkyl group is t-butyl or --C(CH.sub.3).sub.2 CH.sub.2 CH.sub.2 C(CH.sub.3).sub.2 --. Similar disclosures are found in U.S. Pat. No. 3,344,126 and Canadian Pat. 775,576. While the monoperoxycarbonates are broadly claimed in some of these patents, none of the invention compounds are reported.
There is a commercial need for free-radical initiators for use in polymerizing vinyl monomers which have activity between that of t-butyl peroxybenzoate (an industry standard peroxide used in ethylene, styrene and other vinyl polymerizations) and that of dibenzoyl peroxide (a lower temperature industrial initiator). Usually polymerization reactor design, and hence heat removal capacity, fixes the cycle time for commercial polymerization processes. Thus, if it is wished to vary the molecular weight (and consequently the physical properties) of the polymer produced, one changes the temperature of the process and selects a free-radical initiator which will decompose at a rate such that the cycle time of the process remains essentially the same. If it is desired to increase the molecular weight of a polymer such as polystyrene, a lower polymerization temperature can be selected and a free-radical initiator with a lower half-life can be employed to bring about the polymerization. Conversely, if one wants to decrease molecular weight, a higher temperature can be selected and an initiator with a greater half-life can be employed. The 10 hour half-life for dibenzoyl peroxide is at about 70.degree. C., whereas that for t-butyl perbenzoate is about 110.degree. C. Hence a large gap in 10 hour half-life activity temperature exists between these two commercially used free-radical initiators. The initiator needed should also be a liquid for ease of metering into the polymerization reactor (dibenzoyl peroxide is a solid) and should be at least as efficient (preferably more so) in polymerizing vinyl monomers as t-butyl peroxybenzoate.
There is also a need commercially for a free-radical curing catalyst for unsaturated polyester resins which will have greater activity (be faster) than t-butyl peroxybenzoate (also used commercially for curing polyester resins) and OO-t-butyl O-isopropyl monoperoxycarbonate (a known monoperoxycarbonate) and will have activity similar to that of dibenzoyl peroxide (an industry standard). The curing catalyst should desirably be a liquid for ease of dissolution in the curable resin. Since dibenzoyl peroxide is a solid (melting point 106.degree.-108.degree. C.), a liquid curing catalyst with similar activity would be advantageous.